Endothelium-dependent vasodilation plays an important role in the control of coronary vascular tone. An endothelium-derived hyperpolarization factor, epoxyeicosanoids (EETs) and an endothelium- derived relaxation factor, nitric oxide (NO) have been reported to activate K+ channel in vascular smooth muscle and dilate coronary vessels. However, the mechanism by which EETs and NO activate K+ channels remains unknown. Recently, several important observations suggest that intracellular ADP-riboses may serve as a new second messenger to regulate cell functions in non-vascular tissues. Our preliminary findings also indicate that cyclic ADP-ribose and ADP- ribose may participate in the gating of K+ channel in coronary vascular smooth muscle and EETs alter the metabolism of these signaling nucleotides. The purpose of the proposed studies is to determine the role of cyclic ADP-ribose and ADP-ribose in the gating of potassium (K+) channels in vascular smooth muscle cells isolated from small coronary arteries and the contribution of these nucleotides to the effect of endogenous vasodilators such as EETs and NO, on K+ channel activity and vascular tone. We will first characterize the enzymatic pathways of cADP-R and ADP-R metabolism in coronary vascular smooth muscle and define the kinetic properties and regulatory mechanism of the key enzymes in these pathways. These novel nucleotides will be measured using ion-pair reverse phase HPLC technique and their structure will be identified using mass spectrometry. A lymphocyte differentiate antigen, CD38 which has multiple activities including the production and hydrolysis of cyclic ADP-ribose will be detected in vascular smooth muscle of coronary arteries. We will determine the role of cyclic ADP-ribose and ADP-ribose in the gating of K+ channels and define the type of K+ channels that is gated by cyclic ADP-ribose and ADP-ribose using patch clamp technique. We will also explore the molecular mechanism by which cyclic ADP-ribose and ADP-ribose gate K+ channels. Finally we will determine whether cyclic ADP-ribose or ADP- ribose contributes to the effect of endothelium-derived vasodilators. The role of cyclic ADP-ribose and ADP-ribose in K+ channel activation induced by EETs and NO will be examined. These studies will demonstrate a new signaling pathway for the action of endothelium-derived vasodilators and contribute to our understanding of cellular and molecular mechanism gating K+ channels and regulating coronary vascular tone.